It is customary today to use pre-prepared dialysing fluid concentrates to produce dialysing fluid for hemodialysis units, whereby the concentrate is diluted with water in the dialysis unit. In dialysis centers, dialysing fluid concentrates are made available either as pre-prepared products in canisters or bags or they are delivered via a ring piping system from a central tank.
The dialysing fluid is fed to the dialyser of the dialysis unit, which is divided by a semi-permeable membrane into a dialysing fluid chamber and a blood chamber. While the patient's blood flows continuously through the blood chamber, the dialysing fluid flows continuously as a counter-current through the dialysing fluid chamber.
Dialysing fluid concentrates supplied from a central source are easy to handle but have the disadvantage that they cannot be matched to the needs of an individual patient. Concentrates not provided from a central source permit adjustment of the dialysing fluid to suit individual patients but they must then be delivered to the dialysis unit in canisters or bags for each instance of dialysis treatment. In a normal situation it is necessary to use a canister with 5 or 6 liters of acid concentrate and a bag containing 650 to 750 g of sodium bicarbonate.
Since centrally-prepared concentrates can be drawn upon as necessary, no residual material arises, whereas pre-prepared concentrates intended for only a single treatment tend not to be used up. However, correct disposal of the packaging materials by granulation or combustion is only possible after the canister or bag has been completely emptied with the consequence that any residual material left in the canister or in the bag after treatment must be discarded. Furthermore, the disposal of the excess quantity of concentrate to waste constitutes a material loss.
A variety of types of equipment for the preparation of the dialysing fluid from concentrates and water is known. U.S. Pat. No. 4,895,657, for example, describes proportioning equipment in which two fluid concentrates are made available in concentrate containers, each fluid then being mixed and diluted with water in a pre-set ratio. Normally the concentrates are described as “35-fold”, i.e. to a given volume of concentrate sufficient water is added so that the total volume is 35 times that of the concentrate. In practice this means that 1 part by volume of concentrate and 34 parts by volume of water are mixed together.